Injection molding is one of well-known techniques for the preparation of sintered zirconia. More particularly, sintered zirconia is prepared by blending zirconia powder with an organic binder to form a molding composition and injecting the composition into a mold to form a green body of predetermined shape, followed by binder removal and firing. A key in this method is to impart appropriate fluidity to the molding composition in order to fill the mold cavity with the composition by injection. It is also important that the green body have a sufficient green strength to release from the mold, that is, the green body be self-sustaining.
Therefore, the organic binders should be easily burned off and impart fluidity and self-sustaining property to such ceramic molding compositions containing zirconia powder. Such commonly used organic binders are given below.
(a) hydrocarbon waxes such as paraffin wax PA0 (b) plasticizers including phthalates such as dioctyl phthalate, dibutyl phthalate, diethyl phthalate, etc. and adipates such as dioctyl adipate, dibutyl adipate, etc. PA0 (c) deflocculants such as aliphatic amines PA0 (d) dispersants such as cationic, anionic and nonionic surface active agents PA0 (e) oils such as mineral oil, tung oil, and coconut oil PA0 (f) low molecular weight compounds such as fatty acids fatty acid esters, and alkyl alcohols PA0 (g) thermoplastic resins such as polyacrylic resin, polystyrene, polypropylene, polyethylene, polyamide, and ethylene-vinyl acetate copolymers PA0 (a) hydrocarbon waxes such as paraffin wax, PA0 (b) plasticizers including phthalates such as dioctyl phthalate, dibutyl phthalate, diethyl phthalate, etc. and adipates such as dioctyl adipate, dibutyl adipate, etc., PA0 (c) deflocculants such as aliphatic amines, PA0 (d) dispersants such as cationic, anionic and nonionic surface active agents, PA0 (e) oils such as mineral oil, tung oil, and coconut oil, PA0 (f) low molecular weight compounds such as fatty acids, fatty acid esters, and alkyl alcohols, and PA0 (g) thermoplastic resins such as polyacrylic resin, polystyrene, polypropylene, polyethylene, polyamide, and ethylene-vinyl acetate copolymers.
However, in preparing molding compositions by adding these organic binders to zirconia powder and blending the mixture, it is very difficult to find a compromise among fluidity, self-sustaining and binder removal parameters. More particularly, if the molding composition is well self-sustaining, then it suffers from fluidity and binder removal problems. If the molding composition is well flowing, then it suffers from binder removal and self-sustaining problems. The compatible composition of the binder substantially varies with the identity of zirconia powder.
Although the prior art injection molding zirconia compositions were intended to improve their fluidity, self-sustaining and binder removal properties in harmony as described above, with the use of conventional zirconia powder, it was very difficult to find a balanced profile of fluidity, self-sustaining and binder removal properties. No satisfactory sintered zirconia bodies were manufactured.